Filament wound container



1964 E. c. UHLIG ETAL 3,144,952

FILAMEJNT WOUND CONTAINER Filed June 15, 1960 2 Sheets-Sheet 1 A .TTORJVEY Aug. 18, 1964 E. c. UHLIG ETAL 3,144,952

FILAMENT WOUND CONTAINER Filed June 15, 1960 2 Sheets-Sheet 2 A T 1' ORNEY United States Patent Ofiice 3,144,952 Patented Aug. 18, 1964 3,144,952 FILAWNT WOUND CONTAINER Edwin C. Uhlig, Warwick, and Henry C. Buffington, Cranston, RI, llrving A. King, Bellingharn, Mass, and Arnold C. Brooks, Tiverton, 11.11., assignors to United States Rubber Company, New York, N.Y., a corporation of New Jersey Filed June 15, 1960, Ser. No. 36,396 13 Claims. (Cl. 22tl3) This invention relates to filament-wound structures which are used chiefly as pressure vessels, and to methods and apparatus for winding them.

Filament-wound structures comprising glass filament windings and epoxy resin binders are known and used today, and are described in United States Letters Patent No. 2,843,153, granted July 15, 1958, and in three articles entitled History and Potential of Filament Winding, Development of Improved Filament-Wound Pressure Vessels a Study of Filament-Winding Variables and Filament-Winding Developments appearing in the preprint book of the thirteenth Annual Technical & Management Conference, Reinforced Plastics Division, Society of the Plastics Industry at Chicago, Illi nois, February 4, 1958 (Society of the Plastics Industry, 250 Park Avenue, New York, New York) at Section 15-C, pages 1 through 6, Section IS-B, pages 1 through 8 and Section l-D, pages 1 through 10, respectively.

The instant invention relates to such structures, chiefly used as pressure vessels, that have elongated bodies and at least one bulging end, and it relates to methods of winding these structures as well as to apparatus for winding them.

Prior to this invention these bulging end structures were formed by winding the filaments on helical paths around the elongated body portion as disclosed in the aforesaid patent and the first of said articles, so the windings formed a mesh in which the individual windings were disposed at an angle with each other where they crossed. The arrangement selected was that intended to place the windings solely in tension when the structure was internally pressurized, and consequently the well-known hose equilibrium angle of 5444, see page 11, Goodyear Handbook of Hose (May 1, 1934), between the windings and an axial plane through the crossing point was used in winding the structure.

The instant invention provides an improved structure by using, instead of helical windings, windings of two dilferent types. The first type, which will be called girth windings herein, are known in the art and have been referred to as circular windings, see Section -C, page 5, FIG. 4 of the first cited article, but the term girth winding has been selected in this application and the appended claims to designate these windings because the filament path in the winding is substantially a helix with adjacent turns of the filament strand touching each other. The girth windings are employed primarily to give the structure strength to resist hoop rupture in the elongated body portion.

The second type of winding has not been used heretofore in these elongated structures. These windings extend over the structure as what are referred to herein as great circular windings and are referred to in the appended claims as end windings. A great circular winding is one which lies along a path that passes over both ends and the elongated body portion of the structure, yet does not cross itself during one complete cricuit, and forms, by bounding, a sectional surface through the structure, hereinafter called the surface of the winding, which intersects the longitudinal axis of the structure only once. It will become apparent as this description proceeds that in most of the practical structures each great circular winding will not bound a true plane, for if it did one complete circuit would bring the winding back precisely to the beginning point on the surface of the structure, and it is desirable that one complete circuit bring the winding back adjacent to, or spaced a little distance from, the beginning point, so succeeding windings will develop a hollow three-dimensional body. The deviation of the surface of the Winding from a true plane, as will be pointed out hereinafter, can be the result of a continuous gradual deviation throughout the circuit of the individual winding, or it can result from a slight alteration .in the path of that circuit which takes place in only one part of the circuit.

According to this invention, the great circular Windings must be located so that the surface of the winding intersects each of the ends, i.e., the path of the winding extends over both the ends, in each circuit around the structure, and the winding forms an angle at each point on the elongated body portion with the line formed on the surface of the structure by an axial plane thereof through the point of measurement which angle is less than the angle whose tangent is one-half the quotient of the circumference of the body portion divided by the length of the body portion.

By employing these two types of windings, greater flexibility in design in terms of strength to weight ratio at various parts of the structure is possible, more efficient winding patterns over the ends may be obtained, and substantially all parts of the structure may be wound at constant and materially higher tension in the winding strand than was used heretofore.

The invention also contemplates a means designed to apply these windings in an efiicient and economical manner in which a girth winder, a great circular winder carried on an orbital track, and means for moving the form on which the structure is to be wound are combined.

These and other features of the invention will in part be more fully pointed out in, and will in part be apparent from, the following detailed description of specific embodiments thereof and the appended claims, when read in conjunction with the accompanying drawings forming a part hereof, wherein:

FIG. 1 is a schematic side elevation of a filamentwound structure embodying this invention;

FIG. 2 is a schematic top plan view of the structure of FIG. 1;

FIG. 3 is a schematic view illustrating the curing of the structure;

FIG. 4 is a schematic side elevation illustrating winding apparatus according to this invention; and

FIG. 5 is a schematic plan view of the apparatus shown in FIG. 4.

The filament-wound structure 10 illustrated in the drawing is a hollow structure in which the walls are formed substantially entirely of filaments and a binder. Filaments of various materials can be used to produce this structure. For example, ceramic filaments, steel wire, etc., can be used. And various binders can be used. For example, plastic binders can be used. But today the filaments most commonly employed are glass filaments, and the binder most commonly employed is an epoxy resm.

The structure It) includes an elongated cylindrical body portion 11 and two bulging, ovaloid ends 12 and 13. A pair of annular axial, or polar, fittings 14, 15 give access to the interior of the structure through the ends 12, 13 respectively. The structure can be made in various sizes, and in the embodiment illustrated the diameter of the cylindrical body portion equals approximately one-half the overall length of the structure between end fittings.

As will become apparent hereinafter, this structure is produced by winding strands of continuous glass filaments impregnated with the binder resin onto a form, and the arrangement and manner in which these windings are wound into the structure are important elements of the instant invention. In FIGS. 1 and 2 only a few of these windings are segregated, so the invention may be illustrated clearly.

One embodiment of the structure is produced by first completely covering a form, except for the openings for the end fittings 14, 15, by a multiplicity of great circular windings, two of which are designated by the reference characters 16 and 17 respectively. In FIG. 1 only those portions of these windings appear which lie in the part of structure visible in this figure. In FIG. 2 those portions of each of windings 16 and 17 which pass over the end 13 appear in shadow line, but that part of winding 16 which passes over the end 13 is indicated by the reference character in this figure, and that part of winding 17 which passes over end 13 is indicated by the reference character 17 in this figure.

As will be apparent from FIG. 2, winding 16 at one point is substantially tangent to a circle 18 on end 12; circle 18 might be considered the outer periphery of fitting 14 although this need not necessarily be the case. If winding 16 be considered to start at this point of tangency it will progress downwardly as seen in FIG. 2 (toward the observer as seen in FIG. 1) over the ovaloid end 12 and to the cylindrical body part 11 of the structure. At that surface of the body part 11 which is exposed to view in FIG. 1 the winding passes downwardly such that it forms an angle at each point on the elongated body part with the line formed on the surface of that part by a plane axial of the form and through the point of measurement which angle is less than the angle whose tangent is one-half the quotient of the circumference of the cylindrical body part divided by the length of that body part. The aforementioned line will appear as a vertical line in FIG. 1, and the angle referred to is the acute angle be tween such a line and the winding at the point of measurement.

The winding 16 then passes across the ovaloid end 13 in a length 16, which as appears in FIG. 2 is tangent to the projection of circle 18 at that end of the structure, but length 16' is disposed tangent to the projection of circle 18 at a nearly diametrically opposed point from the point of tangency of the length of winding 16 that lies on the end 12. Consequently, a surface bounded by this winding would intersect the axis of the structure.

From end 13 winding 16 then passes again to the cylindrical body part 11 on the side hidden from view in FIG. 1 and passes to the ovaloid end 12 in a length that lies on the body part 11 at an angle in the range described above for the angle formed by the length on that surface of the cylindrical body portion 11 that is exposed to view in FIG. 1. It then passes over ovaloid end 12 to a point of tangency with circle 18 that is close to, but is spaced a little distance on the surface of the structure from, the first mentioned point of tangency of the winding 16 with this circle. The winding then continues in nearly a plane tangent to circle 18 at the last point of tangency until it reaches a crossover point with the previous length of winding 16 at which point a complete circuit of the structure might be considered to be completed, and a new winding 17 to begin which is contiguous with the previous winding 16.

It will be apparent that in the embodiment shown the end of winding 16 commences to lap itself slightly and progressively as it nears what might be considered the crossover point, and this lapping continues but to a diminishing extent as winding 17 commences. In the embodiment shown, windings 16 and 17 will finally be substantially parallel with their edges touching, or slightly lapped, in the lengths of each of these windings that lie along the cylindrical body part 11. In this way the winding proceeds with each succeeding winding advanced from the previous winding around the circumference of the cylindrical body portion a distance equal to the width of the winding strand.

Each winding in one complete circuit, that might be thought to commence and end at the crossover point, defines, by bounding, a surface, i.e., the surface of the winding, which is very nearly a sectional plane that passes through the axis of structure 19 only once.

To produce a closed structure, there should be at least one layer of great circular windings in that structure whose angle, as above defined, at the cylindrical body portion is equal to the angle whose tangent is equal to, or less than, one-half of the quotient of the circumference of the smallest axial opening desired through the end of the structure divided by the overall length of the structure. A first winding is placed on the structure at this angle, and succeeding windings are placed on the structure at the same angle, but along the preceding winding.

If an open mesh structure is desired, as frequently is the case for a subsequent winding in a multi-layer structure, the lead distance between subsequent windings can be made greater than the width of the filament strand. This will result in an open mesh structure after one complete traverse around the circumference of the cylindrical body part which traverse would entail a number of great circular windings.

The angle of the great circular windings can be varied, within the limits stated herein, as needed or desired to produce a structure having the strength and other characteristics needed. In general the angles which will be used will fall within the lower, rather than the higher, part of the range. For any structure other than a relatively short, large diameter structure, such as one whose length is about the same as its diameter, this angle will not be above about 30, and angles of about 5 to 20 will be most frequently employed with good results.

It is a characteristic of structures wound according to this invention that when a substantially constant angle is employed at the cylindrical body part and a steady progression is maintained over the ovaloid ends, each succeeding great circular winding crosses the previous great circular winding only at the completion of the winding at the bulging ends, and the pattern of crossing of succeeding windings forms a circle whose center is the longitudinal axis of the structure. One such circle has been illustrated and is designated by the reference character 18. The closest approach of succeeding windings to the longitudinal axis of the structure as the windings pass over the bulging ends is substantially constant for each succeeding winding under these conditions, and the distance is a function of the winding angle and the axial projection of the bulging end.

When a different angle is selected, for example, in succeeding windings in a multi-layer structure, such as the winding illustrated at 20 and 211 in FIG. 2, the winding as it passes over the bulging ends 12, 13 will be spaced a different distance from the axis of the structure, and the pattern of overlap will form a second circle, similar to circle 18, such as that designated at 21 whose center again is the longitudinal axis of the structure but the diameter of the new circle will vary directly with the angle. It will be apparent therefore that the great circular windings may be made to approach as near the axis of the structure as desired without deviating from the path of great circular windings by the simple expedient of varying the angle of the winding. Further, at any distance from the longitudinal axis of the structure, the ovaloid ends can be reinforced by winding great circular windings at an appropriate angle.

The great circular windings can be applied from a carriage orbiting about the structure, and the windings may therefore be applied at constant tension without loss of tension as the winding is wrapped over the bulging ends. It is desirable, and possible, using this invention that relatively high winding tensions be employed for these great circular windings as well as for the girth windings. Generally, tensions equivalent to tensions in excess of 10,000 p.s.i. on the filament will be used, and preferably tensions equivalent to tensions of 18,000 p.s.i. or more will be used. These high tensions should be maintained throughout the winding operation.

In addition to the great circular windings, the cylindrical body portion 11 is wound with girth windings such as that illustrated at 22 which lie along a helix. Preferably this helix has a pitch such that each succeeding turn of the girth winding touches the next preceding turn, so the number of girth windings to completely cover the cylindrical body portion will equal approximately the length of the cylindrical body portion divided by the width of the winding strand.

In the structure heretofore described, the great circular windings give the structure strength to resist substantially the expansive axial loads, and the girth windings give the structure strength to resist substantially the hoop stresses.

As further illustrating the invention, the following structure is given.

A filament strand in ribbonlike form, composed of three substrands of twelve ends each of type ECG-150 glass filaments, generally referred to as 150s yarn [see man-made textile encyclopedia, pages 327, 328 (Textile Book Publishers, Inc., Division of Inter-Science Publishers, Inc., New York, New York, 1959)] is used in winding the structure. This ribbon is approximately wide and each of the 36 ends in it is made up of 204 filaments of glass each approximately .00038" in diameter. This ribbon was impregnated with a compatible glass type epoxy resin and led to a building form under 15 pounds tension, i.e., the equivalent of 18,000 pounds p.s.i. tension on the filaments. Great circular windings were commenced in which the angle above referred to on the cylindrical body part was maintained at 8. Sufficient great circular windings were applied to the form to completely cover the same, except for the end openings, and to build a structure whose overall length from end to end was approximately twice the diameter of the cylindrical body portion and the length of whose cylindrical body portion is about /3 longer than its diameter. A second group of great circular windings was applied at an angle of 26 /2 and sufficient windings were applied at this angle to make one complete revolution of the periphery of the cylindrical body part.

Girth windings were next applied to the cylindrical body part 10 using the same type of winding ribbon and resin. Sufficient girth windings were applied to completely cover the cylindrical body part of the form from end to end of this part with windings laid side-by-side. A tension of pounds was maintained on the ribbon of 36 ends throughout the girth winding operation.

The thus formed structure, still on the building form, was enclosed within a bag 24 of suitable impermeable material, e.g., butyl rubber. A vacuum hose 25 was connected between the underside of the bag and a vacuum source (not shown), and the bag was evacuated to delete air from the space between the bag and the structure. Steam under 50 pounds pressure was admitted to the atmosphere surrounding the bag in autoclave 26 and the structure was maintained under this steam pressure for four hours to cure the resin.

The use of the bag or blanket 24 in conjunction with a pressure cure is advantageous in producing a dense structure of improved strength.

Apparatus suitable for producing the structures ac cording to this invention is illustrated in FIGS. 3 and 4. This apparatus comprises a building form 27 on which the structure is to be wound. Form 27 is removably carried on a shaft 28 which extends axially of the form. Shaft 28 in turn is supported for rotation about its own axis. This structure may comprise, for example, a crossaxle 19 disposed at right angles to shaft 28 and having a hole therethrough in which shaft 28 is journaled. This cross-axle is normal to the plane of the paper as seen in FIG. 4 and would be rotatable about its own axis so the shaft 28 and form 27 could be rotated thereby to the position shown in broken line. Means (not shown), for example, a sprocket on the cross-axle driven by a chain from a sprocket on a motor axle, would be provided to rotate form 27 and shaft 28 about the axis of the crossaxle 19 to the full line position or the broken line position shown in FIG. 4 or to positions in between these two, or beyond the broken line position, as desired. Means (not shown), such as a motor supported on the cross-axle 19 with a pinion meshing with a gear fixed to shaft 28, can be provided and the motor driven, continuously or intermittently, to rotate form 27 about the axis of shaft 23 as desired. Preferably form 27 would be rotated intermittently, or be indexed, only when the great circular winding is being applied to one bulging end. Means such as a pair of uprights could support the cross-axle in bearings 51.

An open platform 29 is supported for vertical movement with respect to the building form 27 as indicated by the arrows adjacent platform 29 in FIG. 4. For example, platform 29 may be carried on heads 30 of jacks (not shown) which can be actuated to position the level of platform 29 at the extreme up-and-down position of the left-hand end circle of the cylindrical body part of form 27. This platform 29 has a central opening surrounding the position of building form 27 and this opening is closed, in part, by a template 31. Template 31 in turn has a central opening that is bounded by a rail or track 32, which surrounds the building form 27 and is spaced a little distance therefrom as appears in FIG. 5. This rail 32 carries a carriage 33 for spools of the glass filaments and a resin impregnator for these filaments. The ribbon 34 of glass filaments impregnated with epoxy resin is led under tension imposed by tensioners on carriage 33 to building form 27. Means are provided for advancing the carriage 33 about the building form 27 on rail 32 in an orbital path defined by the rail 32 to apply the great circular windings.

These great circular windings are applied by first tipping the building form 27 so that its axis forms the angle, with the plane of template 31, desired Within the limits described above. Then carriage 33 is traversed about orbital track 32. If desired form 27 may be rotated about the axis of shaft 23 continuously as carriage 33 travels continuously on rail 32 with the speed of the carriage 33 on rail 32 and the rotational speed of form 27 adjusted to produce the desired winding angle. In this event a winding angle would result which is slightly different from the angle between the axis of form 27 and template 31. Al-

. ternatively, and in accordance with the now preferred method, after the form was tipped to the desired angle, the form would be maintained stationary and carriage 33 would make one complete circuit of rail 32. As carriage 33 was winding ribbon on one of the bulging ovaloid ends, the form 27 would be rotated a little angular distance about its axis, or be indexed, and would then be held stationary while carriage 33 completed a second circuit of rail 32. In this manner the winding would proceed until all of the desired windings at that angle had been applied, after which building form 27 could be tipped to a new angle and additional windings applied at that new angle as desired.

Platform 29 carries rails 35 that extend along the length of the building form 27 and parallel to the axis of shaft 28. A girth winding carriage 36 similarly is carried on these rails 35. Girth winding carriage 36 is similar to great circular winding carriage 33, and a ribbon 34 of epoxy resin impregnated glass filaments can be led from carriage 36 to the building form 27. To apply girth windings, building form 27 is positioned in the full line position of FIG. 4 and rotated about the axis of shaft 28. At

the same time carriage 36 is traversed along rails 35 opposite the cylindrical body part of form 27 at such a rate relative to the rotational speed of form 27 to apply the girth windings with the desired spacing, and preferably to apply these girth windings with succeeding windings touching the preceding winding.

The means to traverse carriage 33 may comprise a chain 52 surrounding and generally parallel to rail 32 and spaced outwardly therefrom on a series of idler sprockets 53 carried on shafts normal to template 31. An arm 54 conples carriage 33 to this chain, and one or more sprockets 55 on which the chain is trained is fixed to a shaft 56 that fixedly carries a second sprocket on which a second chain 57 is trained that in turn is trained on the drive sprocket 53 of a motor 59 carried, for example, beneath platform 29. Similarly, carriage 36 could be fixed to a chain 60 trained on sprockets 61, 62 at each end of rail 35 with one of the sprockets 62 driven by the output of a reversing motor 63.

The bulging ends may be reinforced by using a great circular winding technique as, for example, by winding great circular windings on the building form, tying these windings down by a few girth windings near the end or ends of the cylindrical body part, and then cutting away the remainder of the great circular windings which extend over the cylindrical body part. Such reinforcing end windings can be applied to one or both ends, as is obvious, and can be combined, as desired, with various patterns of additional complete great circular windings and girth windings.

Further, the great circular windings need not always be the balanced windings shown in the drawings, i.e., the position of the orbital track may be changed so the circle formed by the windings, such as 18, on one end of the structure has a larger diameter than the circle formed by the same windings on the other end of the structure.

Templates 31 having various sized openings adapted to accommodate building forms of various sizes may be provided, and thereby apparatus adapted to produce structures of various sizes may be provided. When a different size structure is to be produced, the old template can be removed from platform 29 and a new template of appropriate size can be placed in this platform. For this reason also rails 35 should be long enough to accommodate the longest structure it is desired to produce, and desirably these rails may be long enough to apply helical windings over both the cylindrical body part and the bulging ends, so that windings of the type disclosed in the aforesaid patent and the first of the aforesaid articles can be applied by the apparatus should that be desired.

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

l. A filament wound structure having an elongated body portion and a bulging end, comprising filaments and a binder, said filaments being arranged in girth windings along said elongated body portion and in end windings passing over said body portion and over the ends of said structure, each circuit of said end windings lying along a path that passes over both ends and the elongated body portion of the structure, each said path meeting itself only once in each complete circuit of said structure, at least one layer in said structure being composed of a plurality of said circuits of end windings in which each end winding circuit in said layer is contiguous to the immediately preceding and immediately following end winding circuits throughout substantially the entire length of said circuits, each such end winding bounding in one complete circuit a surface which is substantially plane, said substantially plane surface of the end winding passing only once through the axis of the structure, and the length of the end windings on the elongated body portion forming an angle at each point along said length with a line formed by the intersection of an axial plane through the structure and the surface of said elongated body portion which angle is less than the angle whose tangent is equal to one- 8 half the quotient of the circumference of said elongated body portion at an end thereof divided by the length of said body portion.

2. A structure in accordance with claim 1 in which said angle of the end windings is less than approximately 30.

3. A structure in accordance with claim 2 in which said angle of the end winding is between approximately 5 and 20 said structure including a plurality of groups of consecutive end windings, the end windings in each said group being disposed in at least one complete circuit of the circumference of said body portion, said angle for each end winding in each group being the same as said angle for each other end winding in its group.

4. A structure in accordance with claim 2 in which said angle of the end winding is constant along each said length and is the same for all said lengths.

5. A structure in accordance with claim 4 in which the progression of said surface for each said end winding from a plane surface as the end winding progresses is substantially continuous at a uniform rate.

6. A structure in accordance with claim 1 in which said angle of the end winding is the same in all said lengths.

7. A filament wound structure having an elongated body portion and a bulging end, comprising filaments and a binder, said filaments being arranged in girth windings along said elongated body portion and in end windings passing over said body portion and over the ends of said structure, said end windings each lying along a path that passes over both ends and the elongated body portion of the structure, said path meeting itself only once in each complete circuit of said structure, each such end winding bounding in one complete circuit a surface which is substantially plane, said substantially plane surface of the end winding passing only once through the axis of the structure, the length of the end windings on the elongated body portion forming an angle at each point along said length with a line formed by the intersection of an axial plane through the structure and the surface of said elongated body portion which angle is less than the angle whose tangent is equal to one-half the quotient of the circumference of said elongated body portion at an end thereof divided by the length of said body portion, a plurality of consecutive end windings being wound at a given said angle, each end winding wound at a given said angle being substantially tangent to a common circle at the closest approach of said common angle end winding to the point where the longitudinal axis of said structure intersects the ends of said structure, said common circle having said point as its center.

8. A structure according to claim 7 including a plurality of groups of consecutive end windings, the end windings in each said group being disposed in at least one complete circuit of the circumference of said body portion, said angle for each end winding in each group being the same as said angle for each other end winding in its group.

9. A structure according to claim 8 including groups wound at at least two said angles.

10. A filament wound structure having an elongated body portion and a bulging end, comprising filaments and a binder, said filaments being arranged in girth windings along said elongated body portion and in end windings passing over said body portion and over the ends of said structure, said end windings each lying along a path that passes over both ends and the elongated body portion of the structure, each said path meeting itself only once in each complete circuit of said structure, that part of each circuit of an end winding that lies in said body portion and one said end lying in a plane, each such end winding bounding in one complete circuit a surface which is substantially plane, said substantially plane surface of the end winding passing only once through the axis of the structure, and the length of the end windings on the elongated body portion forming an angle at each point along said length with a line formed by the intersection of an axial plane through the structure and the surface of said elongated body portion which angle is less than the angle whose tangent is equal to one-half the quotient of the circumference of said elongated body portion at an end thereof divided by the length of said body portion.

11. A structure in accordance with claim 7 in which said angle is less than about 30 for all said end windings the diameter of the circle for said windings at one end of the structure being the same as the diameter of said circle for said windings at the other end of the structure.

12. A structure in accordance with claim 7 in which said angle is less than about 30 for all said end windings the diameter of the circle for said windings at one end of the structure being diflerent from the diameter of said circle for said windings at the other end of the structure.

13. A filament wound structure according to claim 7 including a plurality of partial end windings extending over an end portion of the structure and over only a little distance of said body portion adjacent to said last mentioned end portion, and girth windings wrapped about said partial end windings Where said partial end windings 1% pass over the body portion of the structure a little distance.

References Cited in the file of this patent UNITED STATES PATENTS 2,718,583 Noland et a1 Sept. 20, 1955 2,791,241 Reed May 7, 1957 2,792,324 Daley et al. May 14, 1957 2,809,762 Cardona Oct. 15, 1957 2,816,595 Hudak Dec. 17, 1957 2,827,195 Kearns Mar. 18, 1958 2,848,133 Ramberg Aug. 19, 1958 2,858,992 Wentz Nov. 4, 1958 2,949,149 Strickland Aug. 16, 1960 2,966,935 Wiltshire Jan. 3, 1961 3,031,099 Wiltshire Apr. 24, 1962 3,047,191 Young July 31, 1962 FOREIGN PATENTS 775,577 Great Britain May 29, 1957 

1. A FILAMENT WOUND STRUCTURE HAVING AN ELONGATED BODY PORTION AND A BULGING END, COMPRISING FILAMENTS AND A BINDER, SAID FILAMENTS BEING ARRANGED IN GIRTH WINDINGS ALONG SAID ELONGATED BODY PORTION AND IN END WINDINGS PASSING OVER SAID BODY PORTION AND OVER THE ENDS OF SAID STRUCTURE, EACH CIRCUIT OF SAID END WINDINGS LYING ALONG A PATH THAT PASSES OVER BOTH ENDS AND THE ELONGATED BODY PORTION OF THE STRUCTURE, EACH SAID PATH MEETING ITSELF ONLY ONCE IN EACH COMPLETE CIRCUIT OF SAID STRUCTURE, AT LEAST ONE LAYER IN SAID STRUCTURE BEING COMPOSED OF A PLURALITY OF SAID CIRCUITS OF END WINDINGS IN WHICH EACH END WINDING CIRCUIT IN SAID LAYER IS CONTIGUOUS TO THE IMMEDIATELY PRECEDING AND IMMEDIATELY FOLLOWING END WINDING CIRCUITS THROUGHOUT SUBSTANTIALLY THE ENTIRE LENGTH OF SAID CIRCUITS, EACH SUCH END WINDING BOUNDING IN ONE COMPLETE CIRCUIT A SURFACE WHICH IS SUBSTANTIALLY PLANE, SAID SUBSTANTIALLY PLANE SURFACE OF THE END WINDING PASSING ONLY ONCE THROUGH THE AXIS OF THE STRUCTURE, AND THE LENGTH OF THE END WINDINGS ON THE ELONGATED BODY PORTION FORMING AN ANGLE AT EACH POINT ALONG SAID LENGTH WITH A LINE FORMED BY THE INTERSECTION OF AN AXIAL PLANE THROUGH THE STRUCTURE AND THE SURFACE OF SAID ELONGATED BODY PORTION WHICH ANGLE IS LESS THAN THE ANGLE WHOSE TANGENT IS EQUAL TO ONEHALF THE QUOTIENT OF THE CIRCUMFERENCE OF SAID ELONGATED BODY PORTION AT AN END THEREOF DIVIDED BY THE LENGTH OF SAID BODY PORTION. 